1. Field of the Invention
The present invention relates to laundry appliances, in particular consumer laundry appliances for washing and/or drying of damp textile articles, such as items of clothing, towels and bed linen.
2. Background
It is known that a number of common substances such as oils (for example linseed oil) and other resins, can ignite spontaneously under certain circumstances, when not handled with proper care. Spontaneous combustion can occur when rags, towels, clothing or other textiles wetted with such oils or resins, auto-oxidise and generate enough heat to reach the ignition temperature of the textiles. Spontaneous combustion can occur without a flame, spark or other external ignition source and can occur under ambient conditions without an additional heat source. The provision of an additional heat source may aid ignition and may also initiate spontaneous combustion of materials which may not ordinarily be vulnerable to this process at normal ambient temperatures. In cases where additional heat is provided, (for example, cotton clothing heated in by an external heat source in a laundry clothes dryer) the increase in ambient temperature increases the rate of oxidisation. When the heat produced by the auto-oxidisation reaction is produced more quickly than it can be lost to the surroundings, it builds up and the temperature may reach the ignition point of the surrounding material. Even if the heat build up is not sufficient to initiate spontaneous combustion, the textiles may become charred and/or produce smoke.
Factors important in the determination of whether an auto-oxidisation reaction will result in dangerous heating and/or spontaneous ignition, are the rate of heat generation, the oxygen supply to the oxidisation reaction and the insulative properties of the surroundings. In order for spontaneous combustion to occur, the air supply must be sufficient to provide enough oxygen to permit the oxidisation process to proceed, but not so great that the heat produced by the reaction is reduced (for example, by convection) to the point where sufficient heat build up cannot occur. Auto-ignition of textiles will most commonly occur where the oils are dispersed in a thin layer through a rag or piece of clothing because the surface area of the oil wetted area is maximised.
The phenomenon of spontaneous combustion of textile articles wetted with fuels known to be vulnerable to this event, presents an obvious risk for laundry appliances where such textile articles are loosely packed in a pile and may be additionally heated. These conditions are well known risk factors influencing the likelihood of dangerous overheating and/or which may then lead to catastrophic loss of property or loss of life due to fire. A higher risk of damage may be present where the user of an appliance such as a clothes dryer, interrupts the normal cycle by opening the door, thereby preventing a cool down cycle (where the heating element is deenergised) from being completed.
Passive safety measures such as smoke detectors, located in rooms and buildings are a known method of sensing an abnormal condition such as a fire. In response to sensed smoke, a warning alarm may be activated to alert people of danger and appropriate action can be taken early. There are to our knowledge, no active or passive safety measures known in the prior art for alerting the presence of a dangerous fault condition such as described above, in the field of laundry appliances.